Erosion protection for wells



April 5 A. v. METLER EROSION PROTECTION FOR WELLS Filed Marc h 30, 1966FIG.

ALVIN V. METLER INVENTOR ATTORNEY Unit States Patent 0 3,379,259 ERGSIONPROTECTTON FOR WELLS Alvin V. Metler, Dallas, Tera, assignor to MobilOil Corporation, a corporation of New York Filed Mar. 30, 1966, Ser. No.538,855 8 Claims. ($3. 166--242) ABSTRACT 9F THE DISCLOSURE relation toperforations in the next adjacent sleeve so that the erosive fluidentering the well is forced to follow a tortuous flow path before itimpinges on the tubing. This changing flow path causes the erosive fluidto decrease its kinetic energy and reduce its impact velocity before itreaches the tubing, thereby reducing erosion of the tubing andincreasing the life thereof.

This invention relates to the production of subterranean fluids throughWells, and more particularly to a system for alleviating erosion ofdownhole well equipment by detrital material contained in suchsubterranean fluids.

In the petroleum industry, downhole well equipment often is subjected toerosion due to the abrasive action of detrital material such asunconsolidated sand grains entrained in petro eum fluids as they enterthe well. This problem most often is encountered in multi-ply completedwells which produce fluids from two or more levels in a well. The mostcommon multi-ply completed wells are dual-completion wells in which oilor gas is produced from two vertically spaced subterranean formations. Aconventional manner of dually producing such formations is to set andcement casing through both formations and then set a casing packerbetween the formations. A tubing string is extended through the packerwith its lower open end landed adjacent the lower productive formation.The casing packer thus effectively seals off the annular space betweenthe tubing and casing and isolates the lower iormation, which is influid communication with the interior of the tubing string. The fluidfrom the lower formation thus flows through the tubing and to thesurface of the well or wellhead separately from the fluid from the upperformation which is produced through perforations in the casing into theannulus between the casing and the tubing string. The fluid from theupper formation flows to the wellhead either directly through theannulus or through an additional tubing string.

The section of well tubing which extends past the upper productiveformation is exposed to the produced subterranean fluid as it enters thewell through perforations in the wall of the casing. The fluid usuallyis under substantial pressure and passes from the productive formationthrough the restricted perforations in the casing at high velocity andin jetted streams. This particularly is true where the fluid beingproduced is comprised primarily of gas. Such fluid often has a contentof sand or other particulate detrital material which impinges againstthe pipe surface adjacent the perforations. Such detrital materialentrained in the incoming fluid abrades and erodes the pipe surface,thus leading to pipe failure, and also intensifying the corrosion of thepipe.

3,379,259 Patented Apr. 23, 1968 In the past, numerous means have beenemployed in attempts to protect tubing surfaces and alleviate theerosion thereof. One technique involves the wrapping of layers of leadaround the tubing on the theory that a malleable material Would absorbsome of the kinetic energy of the detrital material more readily thanthe tubing itself. Alternatively, hard, brittle material such asceramics and glass and resilient materials such as rubber have beenemployed as protective materials for the tubing. While such techniqueshave met with some success, the resilient coatings usually being themost effective, none of these techniques has proven entirelysatisfactory.

In accordance with the present invention, there is provided a new andimproved system for alleviating erosion of downhole well equipment suchas tubing string. A preferred embodiment of the invention is utilized ina well traversing a subterranean formation from which it is desired torecover fluids such as petroleum gases. The Well has a first conduittherein with a perforated interval comprising a plurality ofperforations in the wall thereof. The perforated interval is locatedopposite a subterranean producing formation such as the upper formationin a dually completed well of the type described above. A second conduitsuch as a tubing string is disposed within the first conduit oppositethe perforated interval. In producing the well, fluid normally is flowedthrough the perforated interval in the first conduit and then upwardlywithin the first conduit to the surface of the well. Thus, the outersurface of the second conduit is subject to abrasive action of detritalmaterial entrained in the production fluids.

In carrying out the instant invention, a plurality of laterally spacedbaffle members are interposed between the perforated interval in thefirst conduit and the outer surface of the second conduit. In apreferred form of the invention, the bafile members take the form of aplurality of tubular sleeves extending about the outer perimeter of thesecond conduit. Regardless of the configuration of the baffle members,each baffle member is provided with perforations therein which arestaggered relative to the perforations in the next adjacent of thebaffle members. Thus, the bafile members serve to change the directionof flow of the production fluids and detrital material entrainedtherein. Also, the flow of the jet streams emanating from theperforations in the first conduit are changed from streamline or laminarflow to turbulent flow and the pressure drop between the casing and theouter surface of the production tubing is decreased as the productionfluids pass through the several baffie members. These factors tend todecrease the kinetic energy of the detrital material entrained in theproduction fluids and reduce the velocity of impact thereof on thesurface of the production tubing.

For a better understanding of the present invention, reference may behad to the following detailed description taken in conjunction with theaccompanying drawings in which:

FIGURE 1 is an elevation partly in section of a production well assemblyembodying a preferred form of the invention; and

FlGURE 2 is a horizontal section taken on line 22 of FIGURE 1.

With reference to FIGURE 1, there is shown a wellbore 10 traversing aproductive formation 12 and provided with a first conduit or a casingstring 14. The casing is cemented as indicated at 15 and the casing andsurrounding cement sheath are provided with a plurality of perforations17 which define a perforated interval in the casing as indicated bybrackets 18. Although in most wells in which the present invention isutilized the perforations 17 will take the form of generally circularpassages such as those formed by jet or gun-perforating techniques, itwill be understood that other suitable arrangements may be used. Forexample, the perforated interval may be formed by so-called shopperforated or slotted pipe in which the openings in the casing areformed prior to insertion of the casing in the well.

A packer 19 is disposed between the productive formation 12 and a lowerproductive formation (not shown) in order to isolate these formationsfrom one another so that there is no communication between theseformations within the well. A production tubing string 20 is disposed inthe well as illustrated and extends from the wellhead 21 and is landedat a level (not shown) below the packer 19, usually adjacent the lowerproductive formation. Fluids from the lower porductive formation thusare produced through the interior of the tubin string 20 and carried tothe surface of the well where they pass into a suitable gathering line20a.

A second packer 22 is provided between the tubing string 20 and casing14 at a point above the top of the productive formation 12. A secondtubing string 24 extends from the surface of the well and through thesecond packer 22 as shown. As is apparent from the drawing, the secondtubing string 24 provides a production passage to the surface of theWell for fluids produced from the productive formation 12. At thewellhead, fluids from tubing string 24 are delivered into gathering line24a.

The production equipment thus far described is con ventional and doesnot by itself form any part of the present invention. Also, it will beunderstood that the arrangement thus far described is exemplary only andthat other suitable arrangements may be used. For example, tubing 24 andpacker 22 may be dispensed with and fluids from the productive formation12 may be produced to the surface of the well directly through theannular space between the tubing 20 and the casing 14. Alternatively,tubing string 20 may not extend to the wellhead, but instead mayterminate within or above packer 22, in which case fluid from the lowerformation will pass from tubing 20 into the space between tubing 24 andcasing 14 and thence upwardly to the wellhead. Also, while only a singlecasing string 14 is shown, it will be understood that the well may bepro vided with a plurality of casing strings. For example, the well maybe provided with a suitable conductor pipe or surface string and one ormore intermediate strings as will be understood by those skilled in theart. In addition, while the casing 14 in FIGURE 1 is shown as extendingcompletely to the surface of the well, it will be understood that othersuitable arrangements may be used. For example, the perforated outerconduit may take the form of a liner which is suspended from orotherwise extends into a casing string. Alternatively, the perforatedconduit may take the form of a so-called scab liner which does notextend up into a casing string but simply rests upon the bottom of theborehole and is cemented therein in accordance with conventionalpractices. In this case all or part of the well above the perforatedliner may be encased. Such completion practices are well known to thoseskilled in the art and therefore will not be described further.

In accordance with the instant invention, there is provided in theannulus between the outer surface of tubing 20 and the perforations 17in casing 14 at least two and preferably at least three laterally spacedbaffle members. As shown most clearly in FIGURE 2, the baffle memberspreferably take the form of tubular sleeves 26, 27, and 28 disposed innesting relationship with one another and mounted concentrically aboutthe outer surface of tubing 20.

The sleeves 26, 27, and 28 are held in spaced-apart relationship bymeans of upper and lower plates 30 and 31. Preferably the upper andlower plates are formed integrally as shown in order to form a rigidassembly. This assembly is spaced from the tubing 20 by means of spacingmembers such as are shown at 34 in the drawing. Each of the sleeves 26,27, and 28 is provided with perforations 26a, 27a, 284, respectively,which are staggered relative to the perforations in the next adjacentsleeve 01' sleeves so that a straight line cannot be drawn through anytwo perforations in adjacent sleeves intersecting the surface of thenext inner member at right angles. Thus. fluid emanating from theperforation in one sleeve will impinge against a blank portion of thenext adjacent inner sleeve and fluid flowing into the well throughperforations 17 must follow a tortuous path before it reaches the outersurface of the tubbing string 20. Therefore, any abrasive detritalmaterial which contacts the outer surface of the tubing string 20 doesso at a relativvely low kinetic energy state, thus causing little if anyerosion of the outer tubing surface.

Preferably, the perforations in any given sleeve are staggered relativeto the perforations in all the remaining sleeves as shown in thedrawing. Thus, even though the abrasive action of the incoming detritalmaterial should erode an opening in one of the outer sleeves 26 or 27,this opening still would be in a staggered relationship with theperforations in the next adjacent inner sleeve. For example, it can beseen from an examination of FIGURE 1 that detrital material entrained influid passing through one of perforations 26a in sleeve 26 and impingingupon the area of sleeve 27 generally indicated by reference numeral 36ultimately may erode an opening in this sleeve. However, the openingthus formed would still be staggered with regard to the perforations inthe next adjacent inner sleeve 28. Also, the formation of such anopening due to the abrasive action of the detrital material will in manycases serve to increase further the turbulent flow of the productionfluids within the annulus between casing 14 and tubing 20, thus servingto decrease further the kinetic energy of the detrital materialentrained therein.

In the drawings, the perforations in the outer baffle member 26 areshown staggered relative to the perforations in the casing or outerconduit 14. While this arrangement is preferred, it is often difficult,if not impossible, to achieve due to the difficulties involved indetermining accurately the locations of the perforations 17 and inpositioning the baffle member. Thus, even though an attempt is made toposition the outer baflle member as shown in the drawing, it is likelythat some of the perforations therein may be located opposite the casingperforations. In this case, the remaining baffle or baffles interposedbetween the outer baflle and the tubing are essential to the provisionof a tortuous flow path between the easing perforations and the outersurface of the tubing, As noted above, the preferred embodiment of theinvention comprises three or more baffle members. However, in some wellinstallations, space limitations may be such that only two bafflemembers can be interposed between the tubing and casing. In any case, atleast two baffle members must be utilized in order to achieve the newand improved results of the instant invention.

In a preferred embodiment of the invention, the total cumulativecross-sectional area of the perforations in each of the baffle membersis increased with the proximity of the baffle member to the inner tubing20. Thus, the total perforation area in battle member 28 is greater thanthe perforation area in baflle member 27 which in turn is greater thanthe perforation area in baffle member 26, etc. This may be accomplishedby the provision of perforations of progressively greater diameter asshown in the drawings and/or the provision of increasingly greaternumbers of perforations. That is, baffle member 28 may be provided withmore perforations than baflle member 27, etc. This feature of theinvention tends to equalize the pressure drop between adjacent bafliemembers and between the outermost bafile member and the casing.Preferably, the total cumulative cross-sectional area of theperforations in any given baffle member is about twice the area of theperforations in the next adjacent outer 'baflle member. Thus, the totalcross-sectional area of the perforations in baflle member 27 will beapproximately twice that of the perforations in battle member 26. Thissame relationship also preferably holds true with regard to theperforations in the outermost baffle member and the perforations in thecasing. That is, the total area of the perforations in baffle member 26should be greater than and preferably about twice the area of theperforations 17 in casing 14.

The upper and lower plate members 30 and 31 (FIG- URE 1) preferablyprovide complete closures for the spaces between adjacent baflie membersand the space between the outermost baflie member and the casing 14.Thus, all of the fluid flowing into the well must traverse each bafiiemember. The provision of such closure members at the upper and lowerends of the baffle members insures against the possibility of somedetrital material contacting well equipment such as packer 22 at arelatively high kinetic energy state.

The baffle members may be rigidly mounted on the tubing. For example,the spacing elements 34 may be welded or otherwise secured to the outersurface of the tubing. In this case, of course, it will be necessary toinstall and remove the battle members as a unit with the tubing string.In some instances, it may be desirable to slidably mount the bafliemembers about the outer surface of the tubing 20 and support it on asuitable support member such as packer 19 shown in FIGURE 1. In a wellinstallation in which equipment such as packer 22 and tubing 24 is notpresent, this feature is particularly advantageous in that the bafflemembers may be installed or Withdrawn without running or pulling thetubing string. Thus, as one bafile assembly is depleted it may bewithdrawn from the well by means of suitable wire line apparatus andanother assembly installed simply by lowering it througa the annulusbetween the tubing and easing.

Having described certain specific embodiments of the instant invention,it will be understood that further modifications thereof may besuggested to those skilled in the art, and it is intended to cover allsuch modifications as fall within the scope of the appended claims.

What is claimed is:

1. In a well traversing several formations and adapted for theproduction of subterranean fluids, a system for alleviating erosion ofdownhole equipment, comprising:

a first conduit disposed in said well, said first conduit having aperforated interval adjacent one of said formations comprising aplurality of perforations in the wall of said first conduit adapted forthe passage of subterranean fluids into the interior of said firstconduit;

sealing means positioned within said first conduit below said perforatedinterval to isolate said perforated interval from other of saidformations below said perforated interval;

a econd conduit of a smaller size than said first conduit disposedwithin said first conduit, said second conduit extending from saidsealing means to a point above said perforated interval to establish aclosed flow path through said perforated interval; and

a plurality of laterally spaced baflie members interposed between saidperforated interval in said first conduit and the outer surface of saidsecond conduit, each of said baffle members having perforations thereinwhich are staggered relative to the perforations in the next adjacent ofsaid baflie members.

2. The system of claim 1 comprising at least three of said bafllemembers.

3. The system of claim 1 wherein the perforations in the baffle membernext adjacent said first conduit are staggered relative to theperforations in said first conduit.

4. The system of claim 1 wherein said bafile members comprise tubularsleeves extending about the outer perimeter of said second conduit, saidsleeves being of different sizes and disposed in nesting relationshipwith one another.

5. The system of claim 4 wherein the total cumulative cross-sectionalarea of the perforations in each of said sleeves increases with theproximity of said each of said sleeves to said second conduit.

6. The system of claim 4 comprising at least three of said tubularsleeves.

7. The system of ciaim 6 wherein the perforations in the outermosttubular sleeve next adjacent said first conduit are staggered relativeto the perforations in said first conduit.

8. The system of claim 7 wherein said tubular sleeves are slidablymounted on said second conduit.

References Cited UNITED STATES PATENTS 1.397,836 11/1921 Karns 103-2201,473,644 11/1923 Rodrigo 166-205 1,572,022 2/1926 King 103-2202,035,313 3/1936 Grifiin 166-157 X 2,044,657 6/1936 Young 166236 X2,143,836 1/1939 Anderson 16645 X 2,877,852 3/1959 Bashara 166234 X3,282,341 11/1966 Hodges 166-45 X CHARLES E. OCGNNELL, Primary Examiner.

DAVID H. BROWN, Examiner.

